Building a project database
Before going to the field it is important to store all the data gathered for your study area in a database. If you work for an organisation, the best way is to have spatial database at a server. Here we'll focus on storing the data, project and styles in a GeoPackage that is portable and can easily be shared with others.
Choosing the map projection for your study
First you need to determine the projection that you want to use. If you work for a national project, it's best to work in the national projection. If you can't find out what the national projection is, you can choose a UTM or other global projection that is compatible with the GPS device that you'll use in the field. Check the projections supported by the GPS device prior to the fieldwork and choose the projection.
After choosing the projection, you need to find the EPSG code of the projection:
Also take care of different projections that are used in GIS. Don't get confused with the projection of layers and the on-the-fly reprojection used in your project: